Threats to Pikao

In the “Pikao (or Pingao) the Golden Sand Sedge”

The threats to pikao's continued existence are many and varied however all threats are not equally as great. Currently competition with marram grass and lupin are the greatest threats (particularly in southern regions of New Zealand), followed by damage and browse by stock and rabbits and hares. Threats and damage arising from human recreation and coastal development tend not to be such a problem as many of the areas were these activities occur have already been largely denuded of pikao anyway. However, if dune rehabilitation programmes using natives continue, a greater awareness of the effects of these activities on revegetated pikao and other native species will be necessary.

Marram grass (Ammophila arenaria) is an exotic sand-binder and dune builder and can be found on virtually every beach in New Zealand. It is a silvery green coloured perennial grass, native to the coast of Europe and has been widely introduced around the world as a dune stabiliser1. New Zealand lies within marram's native latitudes of 30 to 63 degrees2 providing a temperate climate that it favours3. Marram suffers from a lack of vigour in warmer climates4 and this has been suggested as a reason why marram is more of a conservation management problem in the cooler southern areas of New Zealand5, as has been the finding in Australia3.

Botanical Information

Marram requires active sand burial to stimulate growth like pikao and both species go moribund where sand movement is limited6. Unlike Pikao however marrram thrives under rapid burial1, surviving rates that would bury pikao making it highly competitive. Consequently, marram tends to dominate areas that accumulate sand rapidly at the expense of pikao7. Those areas where pikao remains may be because they are areas receiving slower burial, which do not favour marram growth7.

Slower burial typically occurs with courser particles at they are more difficult for the wind to transport7. Therefore pikao may be found in areas that feature more course sand and gravel, such as Kaitorete Spit south of Christchurch7. The exact location of maram or pikao dominated dune will depend on the sand source, shape of the beach or embayment and the direction of the prevailing wind7.

Marram's leaf structure and arrangement allows it to trap sand more efficiently than pikao7. It typically forms taller steeper dunes that are more densely vegetated, frequently exclude any other vegetation to form pure marram dunes3. Marram although hardy1,8, may have a lower tolerance to salinity than pikao9,10 which may be as factor that explains differences in pikao and maram dominated dune systems.

Marram grasses primary method of reproduction is vegetative rhizomes6 although it also produces seeds1. The rhizomes are extremely vigorous and can colonise new areas by breaking off (e.g. in a storm event) and establishing in new areas. The rhizomes can remain viable after extended immersion in seawater1, enhancing their colonising abilities.

Marram's Interaction with Pikao

Marram exludes pikao in two ways. Firstly, due to marram's superior sand trapping abilities it is able to deprive pikao of sand causing it to go moribund. Secondly, because marram grows quickly, developing extensive root and rhizome systems it is able to outcompete pikao for moisture, resulting in desiccation on pikao6,7. It has been suggested that this desiccation slows pikao's growth, resulting in burial and death6,7.

Marram as a Conservation Problem

Both marram and lupin are regarded as important threats to pikao11. The Department of Conservation has rated Marram grass 12/12 on its effects on the system, based on ratings for significant change to structure and/or composition of the community; suppression of regeneration of native species; persistence over time and whether it increases the fire hazard12. It has also ranked 18/21 on a biological success rating, based on Maturation rate; seeding capacity; dispersal; establishment/growth; vegetative reproduction; competitive ability and resistance to management12.

Strategic management of marram would need to be site bases, and focus on areas where there is already a large pikao population to maintain to warrant control, as based on criteria outlined in the Department of Conservation Strategic Plan for Managing Invasive Weeds13.

Attempts to control marram are being employed in New Zealand and overseas. Methods being trialled include manual removal (severing the rhizomes and removal of plants), mechanical removal (excavating and the buried), or chemical removal spraying using pesticides14. Roundup has been trialled in California14 and in New Zealand the grass specific herbicide Gallant has been used5,7,8. Trials investigating the effectiveness of Gallant are currently being conducted in Doughboy Bay, Stewart Island15. Previous marram control programmes in Stewart Island are regarded as being an outstanding success5. One drawback to this method is that it also kills native grass species (such as the native sand tussock Austrofestuca littoralis), however preliminary results indicate that a substantial seed back has allowed natural regeneration of these species5. Another drawback to this approach is that other native groundcover species tend to be buried15. However, by eliminating marram the natural geomorhic process are set back in motion, and the natural succession of plants will be re-established and the biota, function and character of the dunelands will be restored15. Regardless of the methods used, repeated and intensive treatment will be required14,15.

Marram's Introduction to New Zealand

It was introduced at the turn of the century as a means to combat a problem of sand erosion and movement threatening productive land3. These problem were a direct result of human disturbances such as fire and damage and uprooting by wandering stock on the native dune systems16. Following observations that the native species were failing to recover from these disturbances, steps were taken by the Ministry of Lands to introduce yellow tree lupin and marram grass to stabilise these areas17. Marram grass and lupin subsequently have become the major sand binders and dune builders in New Zealand and continue be the dominant species used for erosion control and dune stabilisation.

Lupin (Lupinus aboreus) was introduced in conjunction with marram as it as nitrogen fixer to provide a nutrient source for marram allowing it to remain vigorous17. Lupin also negatively interacts with pikao by shading it out18. Because lupin usually occurs with marram, it means that pikao will often face a multitude of competitive pressures, severely hampering its ability to persist.

In the late 1980's lupin in New Zealand suffered an infection by lupin blight, severely affecting the population and offering pikao a respite17. Although lupin has recovered to some extent, the Forest Research has been investigating other nitrogen fixing alternatives, which may see the introduction of further threats from other exotic species to the dune environment19. Moves such as this should proceed with caution and be considered a threat to pikao and other coastal species until proven otherwise. An awareness of this issue should be sought by those managing pikao recovery so they may stay abreast of developments in this area.

The negative impacts of stock have been noted as far back as 1880's20. Stock was observed damaging the structural integrity of pikao dunes, opening them up to erosion and blowouts and requiring the introduction of marram and lupin as measures to protect against this17,20. Fencing of areas of pikao vulnerable is the only management measure that can protect pikao from tramping. Frequently these areas are located on private land (such as in the Catlins), so fencing costs may be meet by the land-owner, although they may instead have to be funded by a coast care organisation or DOC.

Rabbits and hares21,22 and possums18 have both been noted browsing pikao. Plants particularly vulnerable to browse are young plants and pose a major threat to revegetation projects. It appears that older plants (after first flowering) are no longer platable23. Sheep have also been noted browsing pikao, but only when there was no other vegetation available22.

Preliminary investigations are underway to examine the effectiveness of an animal repellent to discourage browsing. This repellent (Treepel) has already been found to be effective for rabbits, possums and hares on pine seedlings24.

Pikao that is threatened by coastal development may be best managed by the RMA3,17 and the associated generation of Regional and District Plans (via identification of sensitive areas that contain stands of pikao). An awareness by local territorial authorities will also need to be exercised when any coastal amenities etc. are developed to ensure areas of pikao are not adversely affected.

Damage can also be attributed to recreational activities. Particularly 4 wheel driving and trail biking, which can badly damage otherwise healthy pikao stands. These activities also exacerbate erosion problems by damaging the structural integrity of the dunes and pikaos ability to trap sand by damaging the plant. Bonfires, barbecues and cigarette stubs all pose a fire risk that threaten pikao stands and people not restricting themselves to walkways causes erosion problems that threaten to bury or expose and desiccate pikao plants.